DESC:TECHNICAL FIELD

The present invention relates to Reliability improvement of an exhaust gas recirculation system for diesel engines by introducing an EGR filter in the circuit and more particularly to a low pressure exhaust gas recirculation system for diesel engines.

BACKGROUND

Present stringent emission norms require maximum reduction of NOx (Oxides of Nitrogen) from the engine and this is achieved by EGR (Exhaust Gas Recirculation), after treatment system etc. The low pressure EGR system is used / implemented in diesel engines by many of the engine manufacturers to reduce NOx emission in order to achieve the current BS-III (CEV-Construction Equipment Vehicle) emission regulation applicable to off-road segments with only EGR cooler in the circuit and without any provision of filtering the exhaust gas emitted from the engine. This unfiltered exhaust gas entering to the engine causes deterioration of engine oil and the cylinder components viz., piston rings, liners and valves. Carbon soot is also deposited on the turbocharger's compressor blade which reduces its life and engine efficiency.

Using EGR in diesel engines has real advantages at low engine load conditions where high air/fuel (A/F) ratios are dominant. At high engine load conditions, A/F ratios are greatly reduced and may reach values as low as 20:1. Low A/F ratios contribute to excessive smoke formation. Recirculating exhaust gas with high soot content, whether at high or low A/F conditions, has adverse consequences on engine durability, lubrication oil quality, and on the service life of exhaust gas recirculation system components. Exhaust gases carry a number of chemical constituents that result from the combustion process. These constituents normally include; unburned hydrocarbons (HC), carbon monoxide (CO), carbon dioxide (CO2), Oxides of Nitrogen (NOx) and Particulate Matter (PM), along with other gases. Most, generally about 90%, of nitrogen oxides emitted from diesel combustion are in the form of nitric oxide (NO).

Referring to Fig. 1, which depicts low pressure exhaust gas recirculation system for turbocharged engines with the exhaust gas recirculated directly between the exhaust and intake manifolds, all components of the EGR system, such as heat exchangers and control valves, are subjected to exhaust gas containing all of the untreated products of combustion. As shown in Fig.1, the low pressure EGR includes only the EGR cooler and EGR valve but not the EGR filter. This current practice leads to severe engine components wear and tear and early engine oil deterioration. The untreated exhaust gas shortens the service life of the EGR system, necessitating frequent cleaning of the heat exchanger surfaces to prevent soot loading, or even closure of the gas flow path through the exchanger, as well as frequent cleaning of the EGR flow control valve to prevent soot accumulation which would avoid proper operation of the valve.

Previous attempts at reducing undesirable products of combustion from exhaust gas in turbocharged engines have primarily been directed to treating the exhaust gas downstream of the turbocharger, with the treated recirculated exhaust gas being introduced upstream of the compressor stage of the turbocharger. Other emission reduction systems have also been directed at reducing NOx and hydrocarbon emissions from the overall exhaust gas discharged from an engine. However, neither of the above described exhaust gas treatment systems have effectively addressed the problem of specifically treating exhaust gas recirculated through a low pressure loop EGR system.

To overcome the afore-mentioned problems, there is a need of introducing a filtration system (the exhaust gas, only which is being re-circulated inside the engine) for the in the existing low pressure exhaust gas recirculation system that will make the system more reliable and promising.

SUMMARY

According to an embodiment of the present invention, there is provided a filtration system for low pressure exhaust gas recirculation system in diesel engine. The EGR system comprises of EGR cooler, EGR valve and filtration system known as EGR filter which allows the exhaust gas from the exhaust manifold to pass through it. The EGR filter traps all the carbon and other solid particles (approx 95%) from the exhaust gas and passes the pure exhaust gas to the engine intake manifold through EGR cooler. As a result, it prevents the engine components such as turbocharger blades, intake valves, cylinder liner, piston rings etc. from damaging and improves the components life. This makes the EGR system more reliable as it reduces the NOx emission more effectively without affecting the engine components life and oil deterioration.

BRIEF DESCRIPTION OF THE DRAWINGS

The other objects, features and advantages will occur to those skilled in the art from the following description of the preferred embodiment and the accompanying drawings.

Fig. 1 is the block diagram indicating the flow of exhaust gas in Low Pressure EGR system in the existing state of art

Fig. 2 is the block diagram indicating the flow of exhaust gas in Low Pressure EGR system according to the present invention

Fig. 3 is the layout of the Low Pressure EGR system implemented on the diesel engine according to the present invention

DESCRIPTION

In the following detailed description, reference is made to the accompanying drawing which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that the embodiments may be combined, or that other embodiments may be utilized and that structural and logical changes may be made without departing from the spirit and scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims and their equivalents.
Various modifications will be readily apparent to persons skilled in the art. The general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the invention. Moreover, all statements herein reciting embodiments of the invention, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future (i.e., any elements developed that perform the same function, regardless of structure). Also, the terminology and phraseology used is for the purpose of describing exemplary embodiments and should not be considered limiting. Thus, the present invention is to be accorded the widest scope encompassing numerous alternatives, modifications and equivalents consistent with the principles and features disclosed. For purpose of clarity, details relating to technical material that is known in the technical fields related to the invention have not been described in detail so as not to unnecessarily obscure the present invention.

Various terms as used herein are shown below. To the extent a term used in a claim is not defined below, it should be given the broadest definition and persons in the pertinent art have given that term as reflected in printed publications and issued patents at the time of filing.

According to preferred embodiment of the present invention, the EGR system is described with reference to low pressure EGR system particularly suited in application to diesel engine vehicles lacking fool proof EGR systems. It may be extended to other systems also such as high pressure EGR system and other stationary diesel engine applications that are used in power generators.

A low pressure exhaust gas recirculation system incorporates an EGR filter as illustrated in Fig. 2 according to an embodiment of the present invention. EGR system is NOx emission control technique applied to light, medium and heavy duty diesel engines. A portion of exhaust gases is recirculated into the combustion chambers. It comprises of one or more EGR control valves, one or more EGR coolers, piping, flanges, gaskets etc. EGR is taken out of the exhaust system downstream/ upstream of the turbocharger and driven into the intake downstream (For LP-EGR) / upstream (For HP-EGR) of the compressor. Exhaust gas discharged from an exhaust manifold is directed through the EGR filter where soot and other carbonaceous matter is retained and filtered exhaust gas is passed through EGR cooler which uses engine jacket water as its cooling medium. Once cooled, the exhaust gas re-circulated along with fresh stream of air from air filter flows into the compressor of turbocharger. Both recirculated exhaust gas and fresh air are compressed and fed into the engine intake manifold.

The EGR filter made up of substrate in the form of honey comb structure and the passage of alternate channels are plugged to arrest the solid particles. Further the substrate is sealed by a mat and the whole unit is placed in a stainless steel structure with suitable mounting aids where the process is called as canning. Hence the exhaust gases pass through this filter will be cleaned when it is coming out of the filter.

The exhaust gas discharged from the combustion chambers of the engine through the exhaust manifold carry certain chemical components that result from the combustion process. These components normally include; unburned hydrocarbons, carbon monoxide, carbon dioxide, and nitrogen oxides along with other chemical compounds. Most of the nitrogen oxides emitted from a diesel engine are in the form of nitric oxide (NO) and nitrogen dioxide (NO2). Nitrogen dioxide reacts with soot, primarily carbon that may have accumulated in the diesel particulate filter and forms carbon dioxide (CO2) and nitrogen (N2), two gases that flow through porous particulate filter walls. Removal of the carbon soot thus keeps the filter continuously clean.

Fig. 3 is the layout diagram of EGR system of diesel engine which is implemented few of the BEML make diesel engine. As per the layout, a required portion of engine exhaust gas passes through EGR filter (DPF) (1) for re-circulation and the particulate matter consisting of soot and carbon components is filtered in this. Further the pure exhaust gas alone (Without any soot, carbon particles and solid dust particles) sent to the EGR cooler (2) to bring down the exhaust gas temperature for better NOx conversion. Finally the required portion of filtered & cooled exhaust gas is sent to downstream of the compressor (Low Pressure side). It indicates the achieved BS III(CEV) norms by adoption of above described EGR system.

The above-described EGR system becomes more reliable and promising on the incorporation of EGR filter. The benefits of said system includes that the improper wear of engine components is avoided. Engine performance is maintained over a long period of time and engine trouble free long run is ensured which will improve the engine reliability.

The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the appended claims.

,CLAIMS:We Claim:

1. A low pressure exhaust gas recirculation system with an EGR filter wherein EGR system is NOx emission control technique applied to light, medium and heavy duty diesel engines in which a portion of exhaust gases is recirculated into the combustion chambers which comprises of one or more EGR control valves, one or more EGR coolers, piping, flanges, gaskets ; EGR is taken out of the exhaust system downstream / upstream of the turbocharger and driven into the intake downstream (For LP-EGR) / upstream (For HP-EGR) of the compressor; exhaust gas discharged from an exhaust manifold is directed through the EGR filter where soot and other carbonaceous matter is retained and filtered exhaust gas is passed through EGR cooler which uses engine jacket water as its cooling medium; once cooled, the exhaust gas re-circulated along with fresh stream of air from air filter flows into the compressor of turbocharger, both recirculated exhaust gas and fresh air are compressed and fed into the engine intake manifold.

2. A low pressure exhaust gas recirculation system with an EGR filter as claimed in claim 1 wherein the EGR filter is made up of substrate in the form of honey comb structure and the passage of alternate channels are plugged to arrest the solid particles in which the substrate is sealed by a mat and the whole unit is placed in a stainless steel structure with suitable mounting aids; hence the exhaust gases pass through this filter will be cleaned when it is coming out of the filter.

3. An EGR system wherein a required portion of engine exhaust gas passes through EGR filter (DPF) (1) for re-circulation and the particulate matter consisting of soot and carbon components is filtered in this; further the pure exhaust gas alone (Without any soot, carbon particles and solid dust particles) sent to the EGR cooler (2) to bring down the exhaust gas temperature for better NOx conversion, finally the required portion of filtered & cooled exhaust gas is sent to downstream of the compressor (Low Pressure side).

4. A low pressure exhaust gas recirculation system with an EGR filter as claimed in claim 1, it prevents the engine components such as turbocharger blades, intake valves, cylinder liner, piston rings etc. from damaging and improves the components life. This makes the EGR system more reliable as it reduces the NOx emission more effectively without affecting the engine components life and oil deterioration.